Such devices are commonly used at cable heads or at telephone distribution frames, in particular for protecting user telephone sets against any voltage surges that might be transmitted by the transmission links that enable the sets to be connected to remote centralizing telecommunications equipment. Such protection is achieved conventionally by interrupting electrical continuity along the two wires of a link, and by grounding the wires in the device, when said device is active.
Document FR-A-2560458 describes a protection device triggered by a lightning arrester overheating. A grounding spring is maintained cocked and not in contact by an insulating fuse pellet. The lightning arrester being heated to above a determined temperature value causes the pellet to melt, at least partially, and causes the spring to perform grounding. Unfortunately, because of the structure of the device, and in particular because of the position of the pellet relative to the lightning arrester that controls it, it is not possible to obtain a response that is as quick and reliable as is necessary.
Document FR-A-2659204 describes a protection device which is also triggered by a pellet melting due to a lightning arrester overheating. However, in that case, the pellet is in direct thermal contact with the lightning arrester, which makes it possible for the response speed characteristics of the device to be better controlled. Unfortunately, as indicated in that document, it is possible, under certain conditions, for the pellet to be softened only, and the response of the device is then not necessarily identical to that obtained when the lightning arrester overheating leads to total and rapid melting.